1. Field of the Invention
The present invention relates to the operation of synchronous motors. More particularly, the present invention relates to a method and apparatus for establishing one or more reference currents for use in operating a synchronous motor.
2. Description of Related Art
The torque produced by a synchronous motor usually contains pulsations of rich harmonics. These harmonics are generally due to imperfect interactions between the magnetic flux of the rotor and stator currents. In many cases, the pulsating torque causes deterioration of machine performance and may produce noise and vibration that can be detrimental to the motor. Much effort has been expended in attempts to solve this torque pulsation problem.
In one approach, the problem is addressed with appropriate motor designs. In particular, the structure of the motor is optimized to reduce the sources of harmonics. For example, the reluctance torque is suppressed by surface mounting of the rotor magnets and skewing of the stator slots.
In another approach, the problem is addressed with innovative control strategies. For example, current inputs to the motor are controlled so that no harmonic torque is produced. This approach has more flexibility than the first approach because a general control methodology, once found, can be applied to motors with various designs. Recently, this second approach has become attractive due to the development and availability of fast power electronics and digital electronics with which more sophisticated control can be realized.